With the scaling down of devices, deposition of dielectric films having good step coverage is desirable. Traditional ALD is a self-limiting process, whereby alternated pulses of reaction precursors saturate a substrate surface and leave no more than one monolayer of material per pulse. The deposition conditions and precursors are selected to ensure self-saturating reactions, such that an adsorbed layer in one pulse leaves a surface termination that is non-reactive with the additional gas phase reactants of the same pulse. A subsequent pulse of different reactants reacts with the previous termination to enable continued deposition. Thus each cycle of alternated pulses leaves no more than about one molecular layer of the desired material. The principles of ALD type processes have been presented by T. Suntola, e.g. in the Handbook of Crystal Growth 3, Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14, Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B.V. 1994, the disclosure of which is incorporated herein by reference.
As described herein, Atomic Layer Deposition (ALD) processes can be used to deposit silicon nitride. ALD provides good step coverage on three-dimensional structures. One form of ALD in particular, Plasma Enhanced Atomic Layer Deposition (PEALD), is well suited for depositing silicon nitride. A common precursor for PEALD is Hexachlorodisilane (HCDS). However, PEALD using HCDS does not exhibit optimal growth rate at low reaction temperatures. Therefore, there exists a need for a PEALD method with enhanced characteristics, e.g. growth rate, at temperatures lower than those at which HCDS is maximally effective.